Support AWS Ruby Lambda with Bazel Rules

[kigster]

According to this guide on packaging Ruby Lambda on AWS, dependencies must be installed invendor/bundle folder using bundle install --path vendor/bundle command.

The Ruby runtime provided is Ruby version 2.5.

In order to be able to support this, we must have a way to grab gem dependencies from ruby_bundle and attach gem folders to vendor/bundle and feed it to pkg_zip rule, together with any source files and the configuration YAML.

Right now we have no easy way to extract gem folders from the external bundle. We also don't know if the gems with native extensions built on the target host will work on AWS against Ruby binary possibly located in another place on the file system. This is important because native extensions often hard-code link paths to the ruby interpreter as can be seen from the following output:

Taken from OS-X:

 1 ❯ otool -L jaro_winkler_ext.bundle
jaro_winkler_ext.bundle:
	/Users/kig/.rbenv/versions/2.6.5/lib/libruby.2.6.dylib (compatibility version 2.6.0, current version 2.6.5)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1281.0.0)